Selected Abstracts

FATIGUE & FRACTURE OF ENGINEERING MATERIALS AND STRUCTURES, Issue 9 2010M. YATOMI
ABSTRACT
Due to the variables and unknowns in both material properties and predictive models in creep crack growth (CCG) rates, it is difficult to predict failure of a component precisely.
A failure strain constraint based transient and steady state CCG model (called NSW) modified using probabilistic techniques, has been employed to predict CCG using uniaxial data as basic material property.
In this paper the influence of scatter in the creep uniaxial properties, the parameter,C* and creep crack initiation and growth rate have been examined using probabilistic methods.
Using uniaxial and CCG properties of C-Mn steel at 360 °C, a method is developed which takes into account the scatter of the data and its sensitivity to the correlating parameters employed.
It is shown that for an improved prediction method in components containing cracks the NSW crack growth model employed would benefit from a probabilistic analysis.
This should be performed by considering the experimental scatter in failure strain, the creep stress index and in estimating the,C* parameter.
[source]

The Effect of NaF In Vitro on the Mechanical and Material Properties of Trabecular and Cortical Bone

ADVANCED MATERIALS, Issue 4 2009Philipp J. Thurner
High doses of sodium fluoride in bones lead to severe softening, by weakening interfacial properties between the inorganic minerals and the organic components, while leaving mineralization unchanged.
This leads to reduction of microdamage and associated stress-whitening pointing to a change in failure mode.
Accordingly, elastic modulus, failure stress, and indentation-distance increase are decreased, whereas failure strain is increased.
[source]

Mechanical and fracture properties for predicting cracking in semi-sweet biscuits

INTERNATIONAL JOURNAL OF FOOD SCIENCE & TECHNOLOGY, Issue 4 2005Qasim Saleem
Summary
Mechanical and fracture properties required for predicting crack development in semi-sweet (,rich tea') biscuits have been experimentally determined.
Pilot-scale biscuits of different fat concentrations were prepared and studied with commercial biscuits at different moisture contents.
Bending modulus, fracture stress and strain were measured using three-point bending tests.
All biscuit types showed considerable dependence on moisture content over a range of 4,12%.
Young's modulus and failure stress showed a uniform decrease and failure strain showed an increase with increasing moisture content.
For pilot-scale biscuits of different fat concentrations, an increase in fat level caused a decrease in modulus and failure stress values; however, the failure strains were very similar for all the fat types.
The testing of the samples with top surface up and top surface down revealed that the sample orientation does not affect the measured parameters.
The measured parameters also did not show any directional dependence within the plane, thus assuring that the assumption of an isotropic material would be valid for modelling.
The mechanical and fracture properties measured in this study will serve as a very useful set of data to predict the stress state and cracking of the checked biscuits.
[source]

Genetic Hypercalciuric Stone-Forming Rats Have a Primary Decrease in BMD and Strength,,

JOURNAL OF BONE AND MINERAL RESEARCH, Issue 8 2009Marc Grynpas
Abstract
Kidney stone patients often have a decrease in BMD.
It is unclear if reduced BMD is caused by a primary disorder of bone or dietary factors.
To study the independent effects of hypercalciuria on bone, we used genetic hypercalciuric stone-forming (GHS) rats.
GHS and control (Ctl) rats were fed a low Ca (0.02% Ca, LCD) or a high Ca (1.2% Ca, HCD) diet for 6 wk in metabolic cages.
All comparisons are to Ctl rats.
Urine Ca was greater in the GHS rats on both diets.
GHS fed HCD had reduced cortical (humerus) and trabecular (L1,L5 vertebrae) BMD, whereas GHS rats fed LCD had a reduction in BMD similar to Ctl.
GHS rats fed HCD had a decrease in trabecular volume and thickness, whereas LCD led to a ,20-fold increase in both osteoid surface and volume.
GHS rats fed HCD had no change in vertebral strength (failure stress), ductibility (failure strain), stiffness (modulus), or toughness, whereas in the humerus, there was reduced ductibility and toughness and an increase in modulus, indicating that the defect in mechanical properties is mainly manifested in cortical, rather than trabecular, bone.
GHS rat cortical bone is more mineralized than trabecular bone and LCD led to a decrease in the mineralization profile.
Thus, the GHS rats, fed an ample Ca diet, have reduced BMD with reduced trabecular volume, mineralized volume, and thickness, and their bones are more brittle and fracture prone, indicating that GHS rats have an intrinsic disorder of bone that is not secondary to diet.
[source]

Osteon pullout in the equine third metacarpal bone: Effects of ex vivo fatigue

JOURNAL OF TEXTURE STUDIES, Issue 1 2005ARTUR ZDUNEK
ABSTRACT
This article presents the influence of cell size and cell wall volume fraction on the failure parameters of potato tuber and carrot tissue.
Confocal scanning laser microscope was used for obtaining images of the cell structure of the tissues.
The mean cell face area and the cell wall volume fraction obtained from the images was compared with work to failure, failure stress, failure strain and secant modulus obtained in a compression test of potato and carrot tissue at two strain rates.
Bigger cells and less amount of cell wall material weakened the tissue, which was visible as a linear decrease in the parameters: work to failure, failure stress and failure strain.
There were differences between potato and carrot in the secant modulus.
For carrot, the secant modulus changed with microstructural parameters, whereas for potato, the secant modulus did not depend on these values.
The strain rate decreases all the failure properties for potato.
For carrot, only the work to failure was affected by the strain rate.
[source]

Effects of Thermal Aging on the Mechanical Properties of a Porous-Matrix Ceramic Composite

JOURNAL OF THE AMERICAN CERAMIC SOCIETY, Issue 3 2002Eric A. V. Carelli
The present article focuses on changes in the mechanical properties of an all-oxide fiber-reinforced composite following long-term exposure (1000 h) at temperatures of 1000,1200°C in air.
The composite of interest derives its damage tolerance from a highly porous matrix, precluding the need for an interphase at the fiber,matrix boundary.
The key issue involves the stability of the porosity against densification and the associated implications for long-term durability of the composite at elevated temperatures.
For this purpose, comparisons are made in the tensile properties and fracture characteristics of a 2D woven fiber composite both along the fiber direction and at 45° to the fiber axes before and after the aging treatments.
Additionally, changes in the state of the matrix are probed through measurements of matrix hardness by Vickers indentation and through the determination of the matrix Young's modulus, using the measured composite moduli coupled with classical laminate theory.
The study reveals that, despite evidence of some strengthening of the matrix and the fiber,matrix interfaces during aging, the key tensile properties in the 0°/90° orientation, including strength and failure strain, are unchanged.
This strengthening is manifested to a more significant extent in the composite properties in the ±45° orientation, wherein the modulus and the tensile strength each exhibit a twofold increase after the 1200°C aging treatment.
It also results in a change in the failure mechanism, from one involving predominantly matrix damage and interply delamination to one which is dominated by fiber fracture.
Additionally, salient changes in the mechanical response beyond the maximum load suggest the existence of an optimum matrix strength at which the fracture energy in the ±45° orientation attains a maximum.
The implications for long-term durability of this class of composite are discussed.
[source]

POLYMER COMPOSITES, Issue 5 2003Yuanheng Zhang
An uninterrupted filament winding process was used to fabricate structures made of polypropylene and glass fiber that provide superior reinforcement to Portland cement structures.
Fabricated polypropylene/fiberglass composite tubes were filled with a cement mixture and some were reinforced with internal tapes.
Three-point bending experiments, microscopic observation, and image analysis were used as tools to study various processing variables and their effect on the mechanical properties of the tubes.
The temperature of the mandrel and wetting strongly affected the composite's mechanical properties.
Increased temperatures diminished the void content within the composite and produced a unique "fuzzy" inner surface for the cylindrical tube.
The development of this "fuzzy" inner surface improved the strength and fatigue properties of the cement filled composite tube by providing efficient load transfer to the glass fibres.
Also the surface to volume ratio of the steel rebar geometry when compared to that of the polypropylene/fibreglass structure explains the superior load transfer to the glass.
It was found that a tube reinforced with 15 internal tapes filled with a cement mixture recorded a maximum tensile stress of 71 MPa (10,000 psi) with excellent damage tolerance, more than a 10-fold increase over the upper bound value for steel reinforced cement obtained from the rule of mixtures.
The tube continued to be load bearing to strains of 0.4, which is more than 40 times the failure strain of glass.
These large failure strains are the result of the shear yielding of polypropylene that coats the glass fibres and allows them to move within the cement.
[source]

High-Strain Shape-Memory Polymers

ADVANCED FUNCTIONAL MATERIALS, Issue 1 2010Walter Voit
Abstract
Shape-memory polymers (SMPs) are self-adjusting, smart materials in which shape changes can be accurately controlled at specific, tailored temperatures.
In this study, the glass transition temperature (Tg) is adjusted between 28 and 55,°C through synthesis of copolymers of methyl acrylate (MA), methyl methacrylate (MMA), and isobornyl acrylate (IBoA).
Acrylate compositions with both crosslinker densities and photoinitiator concentrations optimized at fractions of a mole percent demonstrate fully recoverable strains at 807% for a Tg of 28,°C, at 663% for a Tg of 37,°C, and at 553% for a Tg of 55,°C.
A new compound, 4,4,-di(acryloyloxy)benzil (referred to hereafter as Xini) in which both polymerizable and initiating functionalities are incorporated in the same molecule, was synthesized and polymerized into acrylate shape-memory polymers, which were thermomechanically characterized yielding fully recoverable strains above 500%.
The materials synthesized in this work were compared to an industry standard thermoplastic SMP, Mitsubishi's MM5510, which showed failure strains of similar magnitude, but without full shape recovery: residual strain after a single shape-memory cycle caused large-scale disfiguration.
The materials in this study are intended to enable future applications where both recoverable high-strain capacity and the ability to accurately and independently position Tg are required.
[source]

Mechanical and fracture properties for predicting cracking in semi-sweet biscuits

INTERNATIONAL JOURNAL OF FOOD SCIENCE & TECHNOLOGY, Issue 4 2005Qasim Saleem
Summary
Mechanical and fracture properties required for predicting crack development in semi-sweet (,rich tea') biscuits have been experimentally determined.
Pilot-scale biscuits of different fat concentrations were prepared and studied with commercial biscuits at different moisture contents.
Bending modulus, fracture stress and strain were measured using three-point bending tests.
All biscuit types showed considerable dependence on moisture content over a range of 4,12%.
Young's modulus and failure stress showed a uniform decrease and failure strain showed an increase with increasing moisture content.
For pilot-scale biscuits of different fat concentrations, an increase in fat level caused a decrease in modulus and failure stress values; however, the failure strains were very similar for all the fat types.
The testing of the samples with top surface up and top surface down revealed that the sample orientation does not affect the measured parameters.
The measured parameters also did not show any directional dependence within the plane, thus assuring that the assumption of an isotropic material would be valid for modelling.
The mechanical and fracture properties measured in this study will serve as a very useful set of data to predict the stress state and cracking of the checked biscuits.
[source]

POLYMER COMPOSITES, Issue 5 2003Yuanheng Zhang
An uninterrupted filament winding process was used to fabricate structures made of polypropylene and glass fiber that provide superior reinforcement to Portland cement structures.
Fabricated polypropylene/fiberglass composite tubes were filled with a cement mixture and some were reinforced with internal tapes.
Three-point bending experiments, microscopic observation, and image analysis were used as tools to study various processing variables and their effect on the mechanical properties of the tubes.
The temperature of the mandrel and wetting strongly affected the composite's mechanical properties.
Increased temperatures diminished the void content within the composite and produced a unique "fuzzy" inner surface for the cylindrical tube.
The development of this "fuzzy" inner surface improved the strength and fatigue properties of the cement filled composite tube by providing efficient load transfer to the glass fibres.
Also the surface to volume ratio of the steel rebar geometry when compared to that of the polypropylene/fibreglass structure explains the superior load transfer to the glass.
It was found that a tube reinforced with 15 internal tapes filled with a cement mixture recorded a maximum tensile stress of 71 MPa (10,000 psi) with excellent damage tolerance, more than a 10-fold increase over the upper bound value for steel reinforced cement obtained from the rule of mixtures.
The tube continued to be load bearing to strains of 0.4, which is more than 40 times the failure strain of glass.
These large failure strains are the result of the shear yielding of polypropylene that coats the glass fibres and allows them to move within the cement.
[source]